1. Field of the Invention
The present invention relates to a cryogenic coupler which can be advantageously used to achieve connection and disconnection of passages for a cryogenic medium, such as liquefied helium or liquefied nitrogen, that is to be delivered to a desired location.
2. Description of the Related Art
A cryogenic medium, such as liquefied helium or liquefied nitrogen, is typically under a low temperature within the range of 20-100K. When such cryogenic medium is delivered to a desired location, pipes are used which are formed of a material capable of effectively withstanding the low temperature. Generally, the pipes are connected to each other at the flanges on opposite ends thereof, with bolts and nuts.
The pipe connection with flanges is associated with the problems that, not only the connecting or disconnecting operation is troublesome, but also the disconnection of the pipes is impossible unless the cryogenic medium in the pipe is discharged and the temperature is then allowed to rise to around 260K.
In recent years, couplers of the type shown in FIG. 1 have come to be used, which are designed so that the flow passages can be readily connected or disconnected by a one-touch operation. This type of coupler comprises a socket 2 provided with an interior passage 1 which is in communication with a pipe for the supply medium, and a plug 4 which is removably inserted into an opening 2a at one side of the socket 2 and provided with a passage 3 to be communicated with the passage 1. In use, a sleeve 5 on the outer periphery of the socket 2 is caused to slide against the counter-force of a spring S which is arranged on the inner side of the sleeve 5, so that the free end of the plug 4 can be inserted into, or removed from the opening 2a of the socket 2. The sleeve 5 is then returned by the spring S to its initial position, thereby completing the connection or disconnection of the passages for the supply medium. Such a design makes it possible efficiently to achieve the connection or disconnection of the passages, in a facilitated and reliable manner. This type of coupler is typically provided with check valves 6, 7 in the passages 1, 3, which serve to prevent leakage of the supply medium from the socket 2 and the plug 4 even under the presence of the supply medium in the pipes extending to the plug 4 or to the socket 2. This is because the valve bodies 6a and 7a of the check valves are automatically urged against the inner walls of the socket 2 and the plug 4, respectively, by the operation of springs 8 and 9, after the passages have been disconnected from each other.
The conventional coupler described above uses an O-ring P as a seal element between the socket and the plug, for preventing leakage of the supply medium. However, the resilience of the O-ring P tends to be lost due to the shrinkage particularly when the coupler is used under the cryogenic temperature condition. Therefore, it is again difficult to connect or disconnect the socket and the plug to or from each other, unless the supply medium in the passage is removed and the temperature is then allowed to rise to around 260K, as in the case of the abovementioned flanged pipe connection. The duty range of the conventional coupler is from -20.degree. C. to +180.degree. C. in temperature and around 5 MPa in normal pressure, and there are no couplers known at present, that can be used at a lower temperature range.